This invention is directed at externally heating enclosed containers such as aquariums, terrariums and the like using flat etched-foil heating elements.
Typical prior art heating elements were placed inside the tank which resulted in the heater being immersed in water when used with an aquarium. Since these heaters are electrically operated, there is a danger of electrical shock in the event the heater malfunctions. The heaters also take up space in the tank which could have been used for additional fish, scenery, or plants. Additionally the heaters are readily visible and detract from the aesthetic appearance of the tank.
More recent prior art has been directed at flat or relatively thin heating elements disposed on the sides or back of the tanks. One, U.S. Pat. No. 3,842,241, an externally mounted heater, requires a separate temperature controller and temperature sensor. The sensor must be immersed in the water in the tank and requires an additional connection between the sensor and the heater. These external side or back mounted heaters do not detract as much from the aesthetic appearance of the aquarium as do the immersible heaters. When a heater is mounted on the side of an aquarium, it is not generally visible by a person viewing through the front of the tank as long as the Brewster angle is not exceeded. For large aquariums, a side-mounted heater is visible from much of the front wall.
The present invention is located on the outside bottom of the tank where it will not interfere with the aesthetic appearance of the tank.
Prior art heaters, such as the one disclosed in U.S. Pat. No. 4,333,626, utilize resistance rope which tends to sink into the heater insulation. An etched-foil heating element which is used in the present invention does not sink into the insulating layers. Thinner insulating layers may be used allowing thinner heaters. Etched-foil heating elements have considerably more heat transfer area than prior art wire wound or resistance rope heaters. U.S. Pat. No. 4,333,626 specifically teaches the use of a heat transfer plate having an area at least an order of magnitude greater than the heating element. The larger heat transfer area of an etched-foil heating element eliminates the need for a heat transfer plate.
The temperature controllers used in prior art heaters have frequently used thermostats or bimetallic strips. See, for example, U.S. Pat. Nos. 3,890,486, 4,313,048, and 4,333,626. The contact points in these prior art temperature controllers can stick together which will result in overheating the tank and could be a fire hazard. Overheating an aquarium can kill the fish. The present invention uses an electronic temperature controller which eliminates the possibility of overheating due to sticking contact points.